Ocean acidification is already dissolving shells

Posted by Kate Taylor

The first hard evidence has emerged that the shells of marine snails in the seas around Antarctica are being dissolved by ocean acidification.

These tiny animals are a valuable food source for fish and birds - meaning that their decline could affect the entire marine food chain -and play an important role in the oceanic carbon cycle.

In 2008, researchers from the British Antarctic Survey (BAS), the University of East Anglia (UEA), the US Woods Hole Oceanographic Institution and the National Oceanic and Atmospheric Administration (NOAA) examined an area of upwelling, where winds cause cold water to be pushed upwards from the deep to the surface of the ocean.

Upwelled water is usually more corrosive to a particular type of calcium carbonate (aragonite) that pteropods use to build their shells. But with the extra influence of ocean acidification, found the team, this water was corrosive enough to dissolve the shells of pteropods.

"The corrosive properties of the water caused shells of live animals to be severely dissolved and this demonstrates how vulnerable pteropods are," says Dr Nina Bednaršek of the NOAA.

"Ocean acidification, resulting from the addition of human-induced carbon dioxide, contributed to this dissolution."

A number of laboratory experiments have shown how ocean acidification, caused by the uptake of carbon dioxide from the atmosphere, can affect marine organisms. However, this is the first strong evidence of such impacts in the wild.

"Climate models project a continued intensification in Southern Ocean winds throughout the 21st century if atmospheric carbon dioxide continues to increase. In turn, this will increase wind-driven upwelling and potentially make instances of deep water — which is under-saturated in aragonite – penetrating into the upper ocean more frequent," says Dr Dorothee Bakker from the University of East Anglia.

"Current predictions are for the ‘saturation horizon’ for aragonite to reach the upper surface layers of the Southern Ocean by 2050 in winter and by 2100 year round."